Integrated Breast X-Ray and Molecular Imaging System and Method

ABSTRACT

An integrated tomosynthesis/molecular breast imaging device having improved sensitivity includes tomosynthesis imaging components and molecular breast imaging components. The imaging components may be used individually or in combination to provide a system with improved sensitivity and specificity. Molecular imaging components may be smoothly advanced or withdrawn depending upon the desired imaging mode. The system supports both PET and SPECT imaging and enables SPECT collimation to be modified in accordance with image capture requirements.

RELATED APPLICATIONS

This application is a divisional of pending U.S. application Ser. No.12/422,806 filed Apr. 13, 2009, the disclosure of which is herebyincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to the field of breast imaging and moreparticularly to a system and process for breast imaging which integratesmultiple imaging modalities such as tomosynthesis imaging and molecularbreast imaging into a single imaging device.

BACKGROUND OF THE INVENTION

The quality of a breast cancer imaging technique is frequently evaluatedin terms of its sensitivity and specificity. Sensitivity is the abilityof the imaging technology to detect a cancerous lesion. Specificity isthe ability of the imaging technology to ignore objects in images whichmerely appear similar to lesions. It is thus desirable to use a breastcancer imaging technology that is both sensitive (to ensure thatcancerous lesions are not missed) and specific (to reduce the number ofmedical procedures when no cancer is present).

Mammography is currently the most frequently utilized FDA approvedmethod for breast cancer screening. However, mammograms suffer in boththe area of sensitivity and specificity. During a mammogram, x-rays aredirected at compressed breast tissue to generate one or more images(mammograms) of the breast for review. However, because mammograms aretwo dimensional representations of a three dimensional structure, thesensitivity of a mammogram is compromised due to overlapping structuresin the compressed breast. In addition, the similarity of x-rayattenuation characteristics between breast tissue and cancerous tissueincreases the difficulty of differentiating cancerous lesions frombreast tissue, particularly when imaging dense breast tissue.

Efforts to improve the sensitivity and specificity of breast x-rays haveincluded the development of breast tomosynthesis systems. Breasttomosynthesis is a three-dimensional imaging technology that involvesacquiring images of a stationary compressed breast at multiple anglesduring a short scan. The individual images are then reconstructed into aseries of thin, high-resolution slices that can be displayedindividually or in a dynamic cine mode.

Reconstructed tomosynthesis slices reduce or eliminate the problemscaused by tissue overlap and structure noise in single slicetwo-dimensional mammography imaging. Digital breast tomosynthesis alsooffers the possibility of reduced breast compression, improveddiagnostic and screening accuracy, fewer recalls, and 3D lesionlocalization. Examples of breast tomosynthesis systems are described inU.S. Pat. Nos. 7,245,694 and 7,123,684, commonly owned by the Assigneeof this application. While breast tomosynthesis methods greatly improvethe sensitivity of x-ray cancer screening, specificity issues associatedwith dense breasts remain an issue.

Perhaps the most sensitive breast imaging modality is MolecularResonance Imaging (MRI). However the sensitivity of the MRI modalitynegatively affects its specificity. In addition, the cost of the MRIdevices limits their general deployment. Molecular Breast Imaging (MBI)has advanced considerably in recent years as more clinical data hasbecome available. The clinical advantages of MBI include sensitivitysimilar to that of MRI modalities but with a much better specificity andat a much lower cost

SUMMARY OF THE INVENTION

According to one aspect of the invention it is realized that breastcancer diagnosis may be improved via the introduction of an integratedmulti-modal breast imaging system which combines tomosynthesis imagingcapability with molecular imaging capability in a single, integratedbreast imaging device. Tomosynthesis capability is provided using breastX-ray components capable of performing mammography, tomosynthesis andstereotactic imaging for routing breast cancer screening and diagnosis.The x-ray components generate two-dimensional and three-dimensionalanatomical images based on the absorption of x-rays by the breast.

The integrated device also provides molecular imaging capability viamolecular imaging components capable of imaging a breast using methodssuch as single photon planar imaging, Positron Emission Tomography(PET), and Single Photon Emission Computed Tomography (SPECT). Molecularimaging may be used on its own or in conjunction with x-ray imaging.Molecular breast imaging generates a physiological image of the breastbased on the absorption and decay of radioisotopes that have beeninjected into the breast.

The present invention fuses tomosynthesis imaging capability andmolecular imaging capabilities into a single breast imaging device.Integrating the different imaging modalities into a single imagingdevice may increase the speed and accuracy of diagnosis by enabling theradiologist to tune the diagnostic workflow according to the particularneeds of each patient. For example the radiologist may choose to use onemodality over another depending upon a known anatomical structure (i.e.,density) of the patient's breast. Or the radiologist may use the twodiagnostic imaging methods in sequence to obtain additional informationas needed. For example, if a routine mammogram such as that shown inFIG. 1A, obtained using the x-ray components, suggests the presence of alesion 10, the radiologist may opt to obtain a molecular image of thepatient's breast during the patient's visit. The molecular imageverifies the presence of lesion 10, while also highlighting additionalcalcifications 12, 14, which may have been missed in the x-ray image.The present invention enables tomosynthesis images and molecular imagesto be viewed together on a single display, either side by side (forexample providing both FIGS. 1A and 1B on a display), overlaid, in cinemode, etc. The ability to obtain the molecular image with the sameequipment during a single office visit facilitates registration of theimages, allows comparison of the anatomical and physiologicalinformation of the breast at a slice granularity, allows comparison ofCAD results of the images, increases the speed and accuracy of thediagnosis and thereby reduces unnecessary biopsies and concomitantpatient anxiety.

According to one aspect of the invention, a breast imaging deviceincludes tomosynthesis imaging components for obtaining tomosynthesisimages of an anatomical structure of a breast and molecular imagingcomponents for obtaining molecular breast images of a physiologicalstructure of the breast.

According to a further aspect of the invention, a method of imaging abreast in an integrated tomosynthesis/molecular breast imaging (T/MBI)device includes the steps of compressing the breast, performing atomosynthesis scan of the breast, obtaining a molecular image of thebreast and decompressing the breast

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B are respective x-ray and molecular images of a breast;

FIG. 2 is an exemplary embodiment of a fused multi-modal threedimensional breast imaging system of the present invention;

FIG. 3 is a block diagram of a cross section of the gantry base andreceptor housing of the device of FIG. 2;

FIGS. 4A and 4B are diagrams illustrating gamma ray dispersion fromsingle-photon and positron radioisotopes;

FIGS. 5A and 5B illustrate various embodiments of gamma detectors whichmay be included in the Tomosynthesis/Molecular Breast Imaging (T/MBI)device of the present invention;

FIG. 6 illustrates the positioning of gamma cameras and flow of gammarays during Positron Emission Tomography (PET) imaging;

FIG. 7 illustrates a general structure of a single photon planar gammacamera that may be integrated into the T/MBI device of the presentinvention;

FIG. 8 illustrates various collimators that may be used with the gammacamera of the present invention;

FIG. 9 is a flow diagram of exemplary steps that may be performed duringa combined tomosynthesis/molecular imaging process of the presentinvention;

FIG. 10 illustrates an embodiment of the T/MBI device of the presentinvention with gamma cameras retracted to eliminate interference duringtomosynthesis imaging;

FIG. 11 illustrates an embodiment of the T/MBI device of the presentinvention with gamma cameras positioned for molecular imaging;

FIG. 12 illustrates the T/MBI device in a radiology suite;

FIG. 13 illustrates a dual head molecular breast imaging systemincluding slanted collimators;

FIGS. 14A and 14B illustrate alternative collimator arrangements thatmay be used for lesion detection;

FIG. 15 illustrates a dual head molecular breast imaging arrangementwith slanted collimators and its use for mammographic imaging;

FIG. 16 is a side view of a dual head MBI system, provided to illustratehow the dual slanted collimator arrangement improves visualization oftissue in the chest wall;

FIGS. 17A and 17B illustrate an alternative collimator design which maybe used to improve sensitivity and tissue coverage for both the axillaand chest wall during MBI; and

FIGS. 18A-18B illustrate exemplary embodiments of dual head molecularbreast imaging cameras for needle biopsies;

DETAILED DESCRIPTION

FIG. 2 illustrates an exemplary embodiment of an integratedTomosynthesis/Molecular Breast Imaging (T/MBI) device 100 of the presentinvention. The T/MBI device 100 integrates x-ray components withmolecular imaging components to provide a breast imaging system havingincreased sensitivity and specificity.

The T/MBI device 100 of FIG. 2 is shown to include a generally C shapedgantry comprised of an x-ray tube assembly 108, a gantry base 106 and areceptor housing 104, each of which is described in detail below. TheC-shaped gantry is slideably mounted on a stand 140 (FIG. 12) via tracks101 for movement along a Y axis to selectively position the gantry forbreast imaging.

X-Ray Tube Assembly 108

The x-ray tube assembly 108 includes an x-ray tube head 118 and a x-raysupport arm 128. The x-ray support arm is pivotably mounted on thegantry base 106 to enable movement of the x-ray tube head 118 about ahorizontal axis 402 for tomosynthesis imaging. For example, during anexemplary tomosynthesis image scan, the x-ray tube head 118 may movefrom a position of −7.5.degree. to a position of +7.5.degree. During thetube movement, a total of 15 exposures are performed, each havingduration between 30-60 ms. The x-ray tube assembly may also obtainmammograms when the x-ray tube head is positioned at zero degrees.

X-ray tube head 118 includes an x-ray tube (not shown) for generatingx-ray energy in a selected range, such as 20-50 kV, at mAs such as inthe range 3-400 mAs, with focal spots such as a nominal size 0.3 mmlarge spot and nominal size 0.1 mm small spot. The x-ray tube target maybe comprised of tungsten and/or one or more of technetium, rhodium,ruthenium and palladium. The x-ray tube may include one or more filterssuch as molybdenum, rhodium, aluminum, copper and tin. In addition, thex-ray tube may include an adjustable collimation assembly selectivelyfor collimating the x-ray beam from the focal spot in a range such asfrom 7.times.8 cm to 24.times.29 when measured at the image plane of anx-ray image receptor included in the system, at a maximum source-imagedistance such as 75 cm. In one exemplary embodiment, the x-ray tube maybe designed with a moving focal spot which counteracts the movement ofthe x-ray tube during tomosynthesis imaging to reduce image blur, suchas is described in U.S. Patent application Ser. No. 61/117,453, filedNov. 28, 2008 and entitled “Method and system for controlling X-rayFocal spot characteristics for Tomosynthesis and Mammography Imaging,”incorporated herein by reference.

Gantry base 106 houses motors or other means for controlling themovement of various components of the T/MBI device 100. For example, thegantry base houses a motor (X-ray source control 304, FIG. 3) whichcontrols the movement of the x-ray support arm 128 during tomosynthesisimaging. In addition, the gantry base houses a motor (Compressionassembly control 306, FIG. 3) which controls the traversal of acompression assembly 110 along the Y-axis as well as a motor(articulated gamma camera control 302, FIG. 3) that controls themovement of an articulated gamma camera 20.

The compression assembly 110 includes a traversing plate 121, acompression arm 132 and a compression paddle 122 which is releasablycoupled to the compression arm 132 via latch 133. In one embodiment,compression paddles of various sizes can be interchanged and positionedproperly in the field of view of the image receptor as described in U.S.Pat. No. 7,443,949, entitled “MAMMOGRAPHY SYSTEM AND METHOD EMPLOYINGOFFSET COMPRESSION PADDLES AUTOMATIC COLLIMATION AND RETRACTABLEANTI-SCATTER GRID,” owned by the present assignee and incorporatedherein by reference. In one embodiment the compression paddle is moldedfrom a radiolucent material and comprises a generally rectangular basefrom which walls extend to define a compression paddle well 50. Thetraversing plate 121 moves up and down along slots 105 in the gantrybase to control the immobilization or compression of a breast placedbetween the compression paddle base and a surface 16 of the receptorhousing 104. The force used to immobilize or compress the breast mayvary in response to a number of different factors, including but notlimited to a mode of imaging (x-ray, MBI), a type of imaging(tomosynthesis, x-ray, stereotactic), an angle of imaging (CC or MLO), asize or thickness of a breast, a density of a breast, etc. As the breastis compressed, the compression paddle 122 may be permitted to tilt sothat a uniform compression is provided across the entire breast.

According to one aspect of the invention, an articulated gamma cameraassembly 20 is also mounted to the traversing plate 121. The articulatedgamma camera assembly 20 includes a support brace 21, a pair of jointedarms 22 and 24, camera mounts 23 and 25 and gamma camera 26. The gammacamera is essentially a photon detector which counts and images photonsemitted from decaying radioisotopes which have been injected into thebreast (either single or dual photon emitting isotopes as will bedescribed later herein). The jointed arms 22 and 24 are coupled to thesupport brace 21 and camera mounts 23 and 25 by motorized gears whichcontrol the advancement of the gamma camera 26 into an imaging position(shown in FIGS. 2 and 11) and the retraction of the gamma camera 26 intoa retracted position (shown in FIG. 10). In one embodiment when thearticulated camera is placed in the imaging position it rests within thecompression paddle well 50 such that an imaging face of the camera 26remains flush against the rectangular base of the compression paddle asthe paddle compresses or otherwise immobilizes the breast The jointedarms 23 and 24 enable the camera to remain flush against the paddle evenwhen the paddle tilts during compression.

In another embodiment, the gamma camera need not remain flush in thecompression plate well, but rather may be pivoted to any angle around anaxis defined by the camera mounts. The pivoting may be manuallycontrolled or motorized. The ability of the articulated gamma camera topivot freely in this manner allows for improved imaging of the chestwall or axilla tissue. In still a further embodiment, the articulatedarms of the gamma camera may be positioned not at the sides of thecamera, as shown in FIG. 2, but closer towards the center of the gammacamera. In a representative embodiment, the pair of arms may be replacedwith a single articulated arm which is coupled to a mount on the top(non-imaging) surface of the gamma camera, allowing the camera to bepivoted in three dimensions.

As mentioned above, the articulated arms control the advancement of thecamera towards an imaging field, and the retraction of the camera awayfrom the imaging field. In one embodiment, the motion of the camera fromthe retracted to the position to the advanced position is controlledsuch that the leading edge of the camera (i.e., the edge facing thepatient) travels along an underhanded arc path (as indicated by thearrow 1200 in FIG. 10). Introducing the gamma cameras into the imagingfield in this manner keeps the camera below the line of vision of thepatient and may therefore reduce patient anxiety. The camera may beretracted from the imaging field with a leading edge (the edge facingaway from the patient) travels in a generally underhanded arcuate pathtowards the device, also indicated by the arrow 1200 of FIG. 10. Ofcourse other methods of introducing the camera into the imaging field,including lowering the camera into the field on a track or from a pivotpoint, may be substituted herein without affecting the scope of thepresent invention in one embodiment, the movement of the camera 26 issynchronized with the movement of gamma camera 115, although this is nota requirement of the invention and other embodiments wherein the camerasare independently advanced and retracted are within the scope of thepresent invention.

Receptor Housing 104

The receptor housing 104 is an enclosed housing for the detectorsubsystem of the T/MBI device. As mentioned above, an upper surface 116of the housing 104 serves as a breast compression plate, or bucky. FIG.2 includes a cut away view of the receptor housing provided solely forthe purpose of describing the internal detector subsystem 117. Thedetector subsystem includes at least a retracting gamma camera 115 and afull field digital detector 114. The retracting gamma camera 115 is aphoton detector which counts photons emitted from decaying radioisotopeswhich have been injected into the breast (either single or dual photonemitting isotopes). The full field digital detector 114 is an x-raydetector such as the amorphous selenium digital detectors described inU.S. Pat. Nos. 7,122,803, 7,233,005 and 7,304,308 owned by the assigneeof the present invention and incorporated herein by reference. It shouldbe noted that the present invention is not limited to systems which useamorphous digital detectors, and other detectors such as scintillatingdetectors may be substituted herein without affecting the scope of theinvention. In one embodiment, the digital detector is adapted formovement within the receptor housing; for example, the digital detector114 may move laterally or pivot about one or more points duringtomosynthesis imaging. Such movement of the detector may be controlledby a rotate/retract control motor 310 (FIG. 3) located within the gantrybase 106.

FIG. 3 is a block diagram of a cross-section of the receptor housing 104and a portion of the gantry base 106 illustrating the detector subsystemin greater detail. As mentioned above, the gantry base houses severalcontrol systems (302-310).

Although the control systems are represented in the figures as discretefunctional blocks it should be recognized that such delineations areprovided merely to facilitate the description of the device and not byway of limitation; it is appreciated that there are numerous differentbut equivalent ways that the functionality may be combined and embodiedthat are within the scope of the present invention.

An anti-scatter grid 111 is shown positioned between the detector 114and the gamma camera 115. As described in U.S. Pat. No. 7,443,949,referenced above, the anti-scatter grid is positioned over the digitaldetector 114 (in position A) during mammography, to reduce x-rayscatter. The anti-scatter grid may be withdrawn for tomosynthesis and/orother x-ray imaging, preferably via motorized retraction of theanti-scatter grid (to position A′) in the gantry base as indicated bydashed line in FIG. 3.

According to one aspect of the invention gamma camera 115 is withdrawnfrom the x-ray imaging field of view prior to x-ray imaging. In oneembodiment, the gamma camera may be withdrawn by retracting the camera115 into the gantry base 106. For example, gamma camera 115 may bepositioned at location G during molecular imaging, but moved to positionG′ for x-ray imaging. The retraction of the gamma camera 115 may bemotorized, or alternatively may be achieved through manual means (i.e.,via a manual lever to slide the camera into the housing). In anotherembodiment, the gamma camera may be withdrawn from the x-ray imagingfield of view by removing the camera from the device 100, for example byejecting the camera or otherwise extracting the camera from at leastpart of the housing 104.

As will be described in more detail later herein, the gamma camera mayalso be rocked or rotated around one or more pivot points, or movedlaterally or vertically for molecular imaging. For example it may bedesirable to rotate the camera towards the patient to better image thechest wall or axilla tissue. The receptor housing is therefore ofsufficient size to house the gamma camera 115, anti-scatter grid 111 anddigital detector 114 and to allow movement of both the digital detectoras well as the gamma camera. The movement of the gamma camera may alsobe controlled by the rotate/retract controller 310.

According to one aspect of the invention rotate/redaction controlfurther includes functionality for motorized retraction of a collimator215 of a gamma camera (for example by moving the collimator fromposition C to C′) or otherwise withdrawing the collimator from themolecular imaging field. For example, like the anti-scatter grid, thecollimators may be moved into the gantry base (either by motor ormanually) or may be ejectable. In still another embodiment, the buckysurface 116 may be hinged to permit manual access to the collimators ofthe gamma cameras, to allow the collimators to be swapped, exchanged,flipped or otherwise modified. The ability to retract or otherwiseremove the collimator in this manner allows a single gamma camera to beused for molecular imaging using both Single Positron Emissionradioisotopes as well as Positron Emission radioisotopes.

The functionality may also be adapted provide motorized exchange acollimator that is disposed over a scintillator/detector structure 315of the gamma camera with different collimator selected from a group ofalternative collimators 1215 stored within the housing. The collimatormay be of a different type, or of the same type but having differentangular collimations. The ability to exchange collimators in this mannerallows the radiologist to customize the camera in accordance with adesired view. In still another embodiment a programmable collimatorcapable of selective modification the collimation angle may be used forcustom imaging.

In still yet another embodiment, the gamma camera can be tilted atvarying angles during the acquisition. For example, the gamma camera 26can be moved away from paddle 122 sufficiently to allow angulation ofthe gamma camera and so acquire views of the breast with differentangles and therefore acquire information that can be used to perform areconstruction such as SPECT or tomosynthesis view of the distributionof radiopharmaceuticals. In this mode, the gamma camera would be placedin a given orientation relative to the breast, and an image acquired fora time interval. The gamma camera would then be positioned in andifferent orientation and a second image acquired. Multiple images ofthe breast are then acquired and these are used in the reconstruction.

X-Ray Imaging

As mentioned above, the T/MRI device is capable of performing both X-rayand molecular breast imaging. During x-ray imaging x-rays emitted froman x-ray source are directed at a body part to be imaged. The x-rayspenetrate the body part and are attenuated differently depending uponthe structures that they encounter. An x-ray detector on the undersideof the body part records the resultant x-ray energy, providing apictorial representation of the x-ray attenuation and associatedanatomical structure of the body part.

In one embodiment, the x-ray system may be configured for mammographicimaging at multiple views (cranio-caudal (CC) and mediolateral oblique(MLO)), tomosynthesis imaging and stereotactic imaging. During mammogramacquisition, the compression paddle can shift automatically depending onthe view to be acquired. For example, the paddle can be centered on thex-ray receptor for a CC view, shifted to one lateral side of thereceptor for an MLO view of one breast and to the other lateral side ofthe receptor for an MLO view of the other breast. In one embodiment, thesize and shape of the paddle can be automatically recognized by thesystem when mounted so that the shifts can be adjusted to the type ofpaddle. The mammographic images (Mp) are captured as two-dimensionalimages which may be stored and/or immediately displayed to theradiologist.

During tomosynthesis the breast is compressed and a plurality oftomosynthesis projection images (Tp) are acquired at respective anglesrelative to the breast. A variety of systems are provided in the art foracquiring breast tomosynthesis image data. The systems may vary in thenumber of projection images that are obtained and the angles at whichthe images are taken, in the path that the x-ray source takes whenobtaining the projection images (arcuate, linear, sine-wave motion,etc.), in a motion of the digital detector (i.e., rocking, rotating,linear movement) and in reconstruction techniques (back-projection,weighted back-projection, etc). The present invention may incorporateany such tomosynthesis system. The projection images are reconstructedinto a plurality of tomosynthesis reconstructed images Tr representativeof breast slices that have selective thicknesses. Any of the Tp, Tr andMp images may be displayed individually or simultaneously on a displayscreen as described in U.S. patent application Ser. No. 11/827,909entitled IMAGE HANDLING AND DISPLAY IN X-RAY MAMMOGRAPHY ANDTOMOSYNTHESIS, incorporated herein by reference. Simultaneous viewing ofthe images may be performed in a variety of ways, including but notlimited to overlaying one image on another, and toggling betweenindividual or overlaid images or using cine mode, or having one imagedisplayed as an inset in another images. Additionally, the two imagesmay be blended together, or a visual slide bar may be provided suchthat, as the bar slides over the image, the image morphs from an imagetaken in a first modality to an image taken in a second modality, wherethe modality may be an x-ray modality (i.e., mammogram or tomosynthesisimage) a PET or SPECT image.

Molecular Breast Imaging

Two types of molecular breast imaging include Single Photon EmissionTomography (SPECT) and Positron Emission Tomography (PET). In bothforms, the body part to be imaged is injected with aradioisotope/radiopharmaceutical. Cancerous cells tend to absorb higheramounts of the radioisotope than non-cancerous cells and therefore theradioisotope collects in areas of cancerous lesions in the breast. Asthe radioisotope decays, gamma rays are emitted from the radioisotope.The gamma rays are recorded by gamma cameras, which essentially countthe photons in the gamma rays. Those areas of the breast which haveabsorbed the largest amounts of radioisotope will emit the largestnumber of gamma rays and have the highest photon counts in the resultantimage. The quality of the image is dependent upon both the radioisotopeand the gamma camera.

One difference between SPECT and PET lies in the radioisotope that isused for imaging. For example, as shown in FIG. 4A, single photon gammaemitters used in SPECT emit a single gamma ray 410 of energy 80-167+ keVemitted from each decay. Single Photon radioisotopes include, forexample, TC-99 mm (found in Sestamibi), TI-201 (Found in ThallusChloride), Xe-133 (Gas), I-123 (IMP), Co-57 (physics), etc. Dual photonPositron Emission Technology (PET) radioisotopes simultaneously emitdual, co-linear gamma rays 412, 414 of energy 511 keV each. Examples ofPET radioisotopes include the F-18 isotope which can be found in FDG.

FIGS. 5A and 5B illustrate two different embodiments of gamma detectorwhich may be incorporated into the T/MBI device of the present inventionfor PET imaging. FIG. 5A illustrates an Anger type gamma detector 500comprised of a scintillator layer 510 and a visible light detector layer512. Visible light rays 505 are generated when a gamma ray 501 strikesthe scintillator. The detectors in layer 512 detect the visible lightrays, with the relative signals of the detectors indicating the locationof origin of the gamma ray. FIG. 5B illustrates a discrete gammadetector 515 which may be used for PET imaging and includes separatescintillators 514 for each detector 516. When a gamma ray strikes thescintillator layer, resulting visible light photons or charges 511 willonly impact a single detector.

Referring now to FIG. 6, during PET imaging two opposed PET gammacameras such as camera 600 and 610 record the gamma emissions. Usinginformation such as the known spacing of the cameras, the location ofthe lesions in three dimensional space may be readily determined andused to reconstruct a three-dimensional image PET-MBIr. According to oneaspect of the invention, this three-dimensional image may be viewed astwo dimensional slabs of selectable thickness together with x-ray images(Mp, Tp, Tr) on a display. The PET-MBIr images may be viewed side byside with the x-ray images, overlaid with one or more of the x-rayimages for toggling between the images of viewing in cine mode, or oneof the PET-MBIr or X-ray images may be inserted in a thumbnail view inthe other image.

Single photon imaging involves detecting the individual photons that areemitted during decay by using a gamma camera. Photons can emergeunscathed, or can scatter. If the photon scatters, the energy changes.In order to determine where the photon emerged from and to ensure thatscattered energy is not erroneously recorded, gamma cameras generallyinclude collimators. FIG. 7 illustrates exemplary gamma camera 700,which may include one of the gamma detectors of FIG. 5A or 5B (such asdetector 500) and a collimator 710. The collimator essentially filtersout scatter, for example causing contributions of rays b and c (emittedfrom lesion 701) to be rejected or ignored. Three dimensional gammaimages, often called Single Photon Emission Computed Tomography (SPECT)are formed by acquiring multiple images from a gamma camera, with eachimage acquired by having the gamma camera arranged at different anglesrelative to the object being imaged.

Collimators are generally formed as holes lead, foil stamped lead ortungsten or lead casts. FIG. 7 illustrates a general parallel hole typecollimator although other types of collimators may be used for differentbreast imaging needs. For example, slanted collimators may be used toprovide Z position measurement for either lesion or biopsy needle withradiotracers. FIG. 8 illustrates various types of collimators that maybe included as part of the T/MBI device 100, including a parallel holecollimator 800, a converging collimator 810, a pin hole collimator 820and a diverging collimator 830. As mentioned above with regard to FIG.2, the collimators may be stored within or near the device 100, andswapped as needed. More details regarding how different collimators maybe used to provide improved chest wall and axilla tissue coverage, aswell as for three-dimensional lesion localization and biopsy isdescribed later herein.

The SPECT camera operates similarly to a two dimensional digitaldetector, capturing a two dimensional projection image SPECT-MBIp ofgamma radiation during each exposure period. A plurality of projectionimages SPECT-MBIp can be obtained by moving the SPECT camera todifferent angular positions relative to the imaged object and collectingphoton information for the exposure period. In a system such as theT/MBI system which includes multiple gamma cameras one or both camerasmay be moved through angular ranges to capture different projectionimages for each exposure period. A three-dimensional volume may bereconstructed from the projection images using techniques such as thosedescribed in U.S. Pat. No. 5,359,637 entitled Self-CalibratedTomosynthetic, Radiographic Imaging System, Method and Device, by Weber,incorporated herein by reference, to provide a three-dimensionalreconstructed data set SPECT-MBIr. According to one aspect of theinvention, this three-dimensional data set may be viewed as twodimensional slabs of selectable thickness together with x-ray images(Mp, Tp, Tr) on a display. The SPECT-MBIr images and SPECT-MBIp imagesmay be viewed side by side with the x-ray images, overlaid with one ormore of the x-ray images for toggling between the images of viewing incine mode, or one of the SPECT-MBIr or X-ray images may be inserted in athumbnail view in the other image.

Workflow

Having described exemplary components of the T/MBI system, an exemplaryworkflow 900 that may be performed to capture both tomosynthesis andmolecular images with a single breast compression will now be describedwith regard to the flow chart of FIG. 9 and the images of the device 100shown in FIGS. 10 and 11. At step 910 a radioisotope is injected intothe breast. At some point thereafter and in accordance with the halflife of the isotope, the breast is ready for imaging. At step 912 thebreast is compressed between the compression paddle and the bucky 116.At step 914 a tomosynthesis scan is initiated and the x-ray sourcetraverses along a path from position Ts to Tf as shown in inset 1100. Asthe x-ray source traverses along the path a number of x-ray projectionimages are obtained. As shown in FIG. 11 during x-ray imaging the gammacameras 115 and 26 are withdrawn such that they do not encroach upon thex-ray field 1000 or block the detector 114. In some workflows, a CCmammogram view may be obtained following the tomosynthesis scan. In suchinstances the anti-scatter grid will extend over the detector 114 priorto imaging.

In the process of FIG. 9 a molecular image is obtained following thetomosynthesis scan without full breast decompression. At step 916 thecompression of the breast may be adjusted for the molecular scan. It isnot a requirement to adjust the breast compression, and thus the step isshown in dashed lines to indicate its optional nature. At step 918 thegamma cameras are moved into position. In one embodiment the gammacamera 26 moves along path 1100 until it rests flush in the compressionpaddle well as shown in FIG. 11. Gamma camera 115 is moved out of thegantry base into position. In certain gamma camera or SPECT embodiments,only one gamma camera or SPECT camera may be provided for positioning.Advantageously the movement and positioning of the cameras is computercontrolled. For example in some embodiments the cameras may differ insize from each other and/or the digital detector. The cameras may bepositioned in response to the detection of suspicious artifactsidentified during the tomosynthesis screen so that the cameras arecentered on any suspicious artifact, or may be positioned at angles tocapture the axilla tissue or better image the chest wall. Thepositioning of the gamma cameras may be automatic, for example inresponse to CAD screening of the tomosynthesis data, or may becontrolled via user input.

At step 920 molecular image data is obtained. For embodiments that usePET cameras the PET image is obtained by positioning the PET camera pairaround the breast for an exposure period. As described above, to obtain3-D image data using SPECT cameras, the camera(s) may be moved tomultiple positions for a defined set of exposure periods. At step 922,when molecular imaging is complete gamma camera 26 may be retraced alongthe path indicated by line 1100 in FIG. 10, and the breast decompressedat step 924. Assuming that radioisotope was administered to bothbreasts, steps 912-924 may be repeated with the alternate breast.

One embodiment shows sequential use of the imaging modalities. This willinclude the x-ray image acquired before the nuclear image. It is alsopossible to reverse the order of the acquisitions, and perform thenuclear acquisition before the x-ray image.

The T/MBI device however is not limited to sequential use of the imagingmodalities. Rather the provision of different imaging modalities in asingle device enables a radiologist to tailor the workflow based on theparticular need of the patient. For example when dealing with patientswith dense breasts which will x-ray with low sensitivity, the deviceallows the radiologist to forego an x-ray in favor of obtaining amolecular image.

It should further be noted that there is no requirement that MBI imaginghave a fixed exposure period. For example, a workflow is envisioned bywhich the entire breast is imaged at low resolution for a short periodto identify areas of high uptake. A subsequent exposure may be obtainedby imaging just the identified region at higher resolution, using aconverging collimator or pinhole collimator, for example, or by movingthe camera in space to center the camera upon the region of interest.

FIG. 12 illustrates the use of the T/MBI device in a radiology suite.The device 100 may be mounted on a stand 140 for patient heightpositioning. The device 100 may be coupled to a workstation 1010,enabling a radiologist to store and review images on display 1020. Asmentioned above the images from the any of the imaging modalitiesincluding x-ray mammogram images, tomosynthesis images and molecularimages may be displayed either individually or simultaneously asprojection images or reconstructed images. The images may be displayedside by side, or overlaid. Controls at the workstation will enable theradiologist to toggle between two-dimensional projection images, thethree dimensional reconstruction or slices from the same or differentmodality. In addition the reviewer may access, either at the workstationor via a separate workstation, Computer Aided Diagnosis tools whichprovide visual indicators of regions of interest on the images. In oneembodiment, CAD results that are obtained from one modality may beoverlaid on images from the second modality; for example mammography CADresults may be overlaid on MBI images or tomosynthesis slices,tomosynthesis CAD results may be overlaid on mammography or MBI resultsor MBI CAD results may be overlaid on any x-ray images. In still afurther embodiment, CAD results are generated based on input from bothimaging modalities.

Dual Head MBI Features

As mentioned above, the device is not limited to breast screening ordiagnostic use or to use in combination with the x-ray imagingcomponents. According to one aspect of the invention, it is realizedthat improved three-dimensional lesion localization and biopsycapability can be provided using a dual-head molecular breast imagingtechnology that is capable of modifying the collimation of the gammarays. The dual-head MBI device may be part of the integrated T/MBIdevice 100 (which, as described with regards to FIG. 3 may change thecollimators that are used with the gamma detector), or may be providedas a discrete dual-head MBI device.

For example FIG. 13 illustrates a dual head MBI imager 1300 having anupper gamma camera 1310 and a lower gamma camera 1320, and obtaining acranio-caudal (CC) image of the patient's breast. The upper cameraincludes a detector 1314 and a collimator 1312, while the lower cameraincludes detector 1324 and collimator 1322. According to one aspect ofthe invention, the collimators 1312, 1322 are both slanted collimatorswhich are positioned adjacent and parallel to each other, with the slantof collimator 1312 being a minor image of the slant of collimator 1322.The slants assist in determining the Z location of the lesion 1330 asfollows. As the radioisotope decays, gamma rays will be emitted fromlesion 1330. The rays are detected at the detector in location b of theupper camera 1310 and at the detector in location a of the lower camera1320. With a collimator slant angle of known value “.theta.”, a knownvalue “d” of the distance between the cameras (and associated breastthickness), the lesion location “h” is derived using equation I below:

h=d2+12*a−b tan .theta.  Equation 1 ##EQU00001##

This equation can be understood conceptually very easily. The locationon the gamma camera a and the angle of the collimator holes allow one todetermine the trajectory line that the photon traveled along to resultin an image at location a. Similarly for the other gamma camera locationb, one can determine the trajectory line. The intersection of these twolines determines the point in three-dimensional space where the lesionis located.

FIGS. 14A and 14B illustrate alternate embodiments of gamma cameras,wherein the collimators 1412 and 1410 differ in that collimator 1412 isa slant collimator of angle “.theta.” while the collimator 1422 is aparallel through hole collimator The collimators of cameras 1450 and1460 differ in that collimator 1452 is slanted at a different angle thanthe collimator 1462. In both instances, the corresponding lesion heightcan be derived using equations similar to that of Equation I but takinginto account the relative difference in collimation angles.

Providing slanted collimators in a dual-head gamma MBI system canincrease the imaging coverage of the system. When performingconventional x-ray breast mammographic imaging, breast tissue outsidethe compression assembly is not visible in the resulting image. However,using a dual-head gamma camera with slanted collimators permits activeimaging of axilla and chest tissue.

For example FIGS. 1 SA and 15B illustrate respective right and leftmedia-lateral oblique (MLO) breast views using the dual slantedcollimators 1510 and 1520. The slanted collimators provide extendedtissue coverage of breast tissue that is outside the active compressionarea of the detector heads. As labeled, region “a” has the full systemsensitivity thereby enabling views of tissue within the chest wall.Regions “b” and “c” will have limited, but not zero, sensitivity,allowing partial sensitivity for tumor detection within the axillatissue. Region “d” has no sensitivity for any tumor detection.

FIG. 16 illustrates a side view of a CC breast compression. In general adetector edge has a finite thickness that limits the detectionsensitivity of the breast tissue along an edge, referred to in FIG. 16as the dead space 1630. The dead space can be as much as 5 to 7 mm. Anytumor that is within the dead space or further within the chest wall isnot imaged with conventional x-ray imaging technology. However an gammacamera with a dual-slanged collimator overcomes the problems associatedwith detector dead space and even enables imaging of breast tissue “a”that extends into the chest wall. As in FIGS. 15A and 155B, use of thedual slanted collimators allows areas “b” and “c” to be imaged with somelevel of sensitivity.

In order to improve tissue coverage of both axilla and the chest wall itis desirable to slant the collimator holes both in the lateral directionfrom left to right and in the nipple to the chest wall direction. FIGS.17A and 17B illustrate respective examples 1700 and 1750 of suchcollimators. In FIG. 17A, one collimator 1700 that is designed to focuson a region of interest via the focusing corner 1710 is illustrated.FIG. 17B illustrates a second embodiment of a custom collimator that maybe arranged to focus on a small region of interest with improveddetection sensitivity. Each of the four collimator segments serves toimage the lesion, and the sensitivity, or number of photons imaged in agiven unit of time, is four times that of a single gamma camera withcollimator pointing at the lesion.

To perform biopsies the dual-head MBI system the design should allowsimultaneous, active tracing of needle location and easy access to thebreast lesion. FIGS. 18A-18D illustrate various embodiments of adual-head MBI system for needle biopsies. In FIG. 18A the cameras 1810and 1820 are of similar size. Once the lesion is located, the needle1830 (coated with tracer material) may be inserted into the breast. Theslant collimators of camera 1810, in conjunction with data received fromcamera 1830, enables active tracing of the needle during the biopsy withreal-time needle trajectory feedback. FIG. 18B illustrates an alternateembodiment, wherein once the lesion location is identified camera 1810is replaced with a smaller camera assembly 1840, which is positionedsuch that the edge of camera 1840 clears the known location of thelesion to allow the biopsy needle to be directed at the lesion.

In the embodiment illustrated in FIGS. 18C and 18D, the top camera 1870is comprised of two smaller detector/collimator assemblies 1870A and1870B in close packaging to serve as a larger size imager. FIG. 18Cillustrates the cameras 1870 and 1820 in an imaging position which isused for lesion localization. In one embodiment, once the lesion isdetected and the location identified, one half of the assembly (1870B)may be removed to provide an arrangement such as that shown in FIG. 18B.According to another embodiment, once the lesion location is detected,the collimator from one half of the assembly (i.e., the collimator 1875from portion 1870B) may be removed and flipped to provide a focusingcollimator arrangement such as shown in FIG. 18D.

Thus it can be seen that the use of one or more slant collimators cangreatly improve viewing coverage of a dual-head gamma camera breastimaging system, providing improved three-dimensional localization andbiopsy capability as well as improved coverage of axilla and chest walltissue. The dual-head gamma camera breast imaging capability may beprovided in a dedicated system, or alternatively as part of the T/MBIimaging system described above with regard to FIGS. 1-13.

The above description thus details the use of a combination x-ray andgamma camera system for use in cancer screening, diagnosis and biopsy.It should further be appreciated that the system may be used to providethree dimensional coordinates of markers, for example such as theTriMark™ Marker provided by Suros System, Inc., a subsidiary of Hologic,Inc. In addition, the system may be used to dynamically track aradioactive needle during a biopsy, for example to perform image guidedsurgery.

Accordingly an integrated multi-modal breast imaging system and methodof use has been shown and described. The system combines tomosynthesisimaging capability with molecular imaging capability in a single,integrated breast imaging device, resulting in a breast imaging systemwith increased sensitivity and sensitivity. Having described exemplaryembodiments of the system, it should appreciated that the above specificexamples and embodiments are illustrative, and many variations can beintroduced on these examples and embodiments without departing from thespirit of the disclosure or from the scope of the appended claims. Forexample, elements and/or features of different illustrative embodimentsmay be combined with each other and/or substituted for each other withinthe scope of this disclosure and appended claims.

1. A method of obtaining a molecular breast image using a gamma cameracomprising a collimator includes the steps of: immobilizing a breast;obtaining a first exposure of the breast to identify a suspect lesion;modifying the collimator of the gamma camera; and obtaining a secondexposure of the breast, wherein the step of modifying the collimatorfocuses imaging on the suspect lesion.
 2. The method of claim 1 whereina first duration of the first exposure is smaller than a second durationof the second exposure.
 3. The method of 1 wherein the step of modifyingthe collimator of the gamma camera is motor controlled.
 4. A method ofobtaining a molecular breast image using a gamma camera comprising acollimator includes the steps of: immobilizing a breast; obtaining afirst exposure of the breast; modifying a position of the gamma camera;and obtaining a second exposure of the breast.
 5. The method of claim 4wherein the step of modifying the position of the gamma camera directsthe gamma camera towards at least one of the axilla and the chest wall.6. The method of claim 4 wherein the step of modifying the position ismotor controlled.
 7. A method of obtaining three-dimensional image dataof a breast using a Single Photon Emission Tomography (SPECT) gammacamera includes the step of: immobilizing a breast that has beeninjected with a radioisotope; obtaining a plurality of molecular imagesof the breast by positioning the SPECT camera at a plurality ofdifferent positions relative to the breast for an exposure period toobtain a plurality of SPECT projection images; and reconstructing theprojection images into a three-dimensional data set for display on adisplay device.